The present invention relates to watchcases, and more specifically to the means of attaching a crystal engaged in a recess formed at the top of a constituent part of the case, such as the body or bezel.
In conventional designs, the crystal is commonly contained in its recess by means of a sealing strip in which it is press-fitted, the seal in turn being seated in the recess. The retention of the crystal is effected by forces due to seal-crystal and seal-bezel or -body friction, and the retention will materially depend on the depth of the recess. But this approach cannot be advantageously employed in watchcases of very small thickness.
To overcome this disadvantage, it has also been proposed that the crystal be fixed in its recess by bonding with an adhesive substance formed of synthetic resins. It is known, however, that the cements ordinarily used have several disadvantages, one of which is that their absorption of the differential thermal expansion that may occur in the material of the crystal and the body or bezel is very poor. Besides, if the adhesion is to be good both on the metal of the body or bezel and on the glass, the bonding surfaces must still be comparatively large.
Accordingly, one object of the invention is to propose a means of fixing the crystal in its recess, permitting a marked reduction of the depth of the recess without endangering the strength of the assembly, be easy in execution and substantially impervious to thermal stress or other aging phenomena to which cements are generally susceptible.
To that end, the invention proposes to achieve a sealing of the crystal into its recess by means of a mass of metallic material arranged in the space bounded by the side walls of the recess and the crystal, the said mass adhering by soldering to the wall of the recess on the one hand and on the other hand exerting a geometrical locking effect on the side wall, specially contoured for the purpose of the crystal.
To facilitate introduction of the metallic mass, the latter may comprise a material capable of exhibiting a liquid or pasty consistency at the time of installation of the crystal and then setting under the ordinary conditions of use of the watch.